In the words of the United States Patent And Trademark Office:
"Since June 8, 1995, the United States Patent and Trademark Office (USPTO) has offered inventors the option of filing
a provisional application for patent which was designed to provide a lower-cost first patent filing in the United States."
"A provisional application for patent is a U. S. national application for patent filed in the USPTO... It also allows
the term "Patent Pending" to be applied."